This invention relates to a radial stacking (stockpiling) conveyor assembly that is utilized to transport material into stockpiles, storage bins, or other places of storage or placement. Conveyors of this type are generally comprised of a conveyor frame or boom, an undercarriage that may consist of a front push arm and a rear push arm, and a wheel assembly. The front end of the conveyor frame may be raised and lowered mechanically or hydraulically, and the conveyor frame is swung slowly about the pivot point at the tail end of the conveyor, travelling on the wheel assembly along an arcuate path. In order for the conveyor assembly to be swingable about the tail end pivot point while at the same time providing for elevation of the conveyor frame to the proper height for moving the material, it is necessary to have a proper mechanism for the raising and lowering of the conveyor assembly. With conveyors of this type, as the conveyor frame is raised and lowered, a constant radius must be maintained between the rear pivot point of the conveyor frame and the radial traveling arc of the wheel assembly. If some suitable arrangement is not provided to compensate for the raising and lowering of the conveyor, the distance between the end pivot point and the arc of the wheel assembly will vary as the conveyor is raised or lowered, or something in the conveyor structure will fail. In the past, this constant radius has been maintained by the use of a straight cam-lever combination employed at the intersection of the rear push arm and the conveyor frame, or in some models of radial stacking conveyors, a proportional lever-arm and pulley mechanism employing a steel cable subassembly at the intersection of the front push arm and the conveyor frame.
The straight cam-lever combination utilizes a straight channel containing a cam slot that is affixed to the bottom of the conveyor frame, which channel parallels the conveyor frame. A lever arm is pivotally affixed to the bottom of the conveyor frame at one end and to the rear push arm at the other end. As the conveyor frame is raised or lowered, the cam follower located at the top of the rear push arm travels back and forth within this straight cam slot. Thus, as the conveyor frame is raised, the cam follower is slidably drawn forward in the cam slot. Similarly, as the conveyor frame is lowered, the cam follower is slidably pushed rearward in the cam slot. This action operates to allow the undercarriage to pivotly move upwardly and downwardly while the distance between the tail end pivot point of the conveyor and the radial traveling arc of the wheel assembly remains constant. However, as the cam follower travels along the straight cam slot, the linear nature of the cam slot does not geometrically correspond with the movements of the rear push arm and the arc of travel of the pivot points of the lever arm. Rather, the cam follower follows a slightly curved path. As a result, movement of the cam follower through the straight cam slot is met with increased resistance as the cam follower is forced against the side of the channel. This action increases the tension upon the structural components of the triangular configuration of the conveyor frame, rear push arm and front push arm, which increased tension increases the structural stresses transferred to these components. These increased structural stresses can operate to induce fatigue failures over the passage of time and use resulting in higher than normal repair costs being incurred by the owner of the conveyor, and further resulting in losses associated with the down time while repair parts are being made.
Another prior art constant pivot mechanism for maintaining the same arc of wheel travel regardless of the height of the conveyor frame involves the use of a proportional lever-arm pulley mechanism which employs fixed steel cables connected to a pivotal lever arm assembly attached to the conveyor frame. The cables travel over pulleys affixed the top of the front push arm. The connection of the front push arm and the conveyor frame sits within a channel in which the top of the front push arm travels as the conveyor frame is raised and lowered. The lever-arm mechanism rotates as the conveyor frame is raised and lowered so as to maintain the proper tension upon the cables. This prior art constant pivot mechanism requires the use of additional material in the construction of the conveyor, such as the steel cables and lever pivot mechanism, thus adding to the cost of producing the unit. Additionally, with the pulley mechanism and tension maintained upon the cables, additional maintenance and repairs are required of the user, further increasing the overall cost of operation. As a result of these cost considerations, the constant pivot mechanism conveyors fell into disfavor in the industry upon the introduction of the straight cam-lever combination conveyors.
Because of the deficiencies in the prior art conveyors of this type, there exists a need for an improved constant pivot mechanism that will provide a simple and relatively inexpensive way to maintain the same arc of wheel travel as the conveyor frame travels throughout its range of height.